modules/rle: consider offseting symbol count by one

[proppy]

per @grebe on #974 and #1006:

I think it is useful to treat count as being offset by 1 so count=0 means 1 symbol, count=1 means 2 symbols, etc. Disallowing count=0 is wasteful when count is narrow, e.g. in the case of count being 1 bit it will always be longer. If you encode count with an offset, it should probably be named something like offset_count or count_minus_one to avoid confusion.

[mtdudek]

In PR #1052 I take advantage of counter value being 0 to indicate invalid pair.
#1052 PR also adds valid signal to the symbols stream.
Decoder is or will be updated to handle and emit empty last packets.
So I would leave count as is, and fix decoder in the near future.